In the recent years, several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and to provide more and better applications and services. The 3rd generation partnership project 2 (3GPP2) developed code division multiple access 2000 (CDMA 2000), 1× evolution data optimized (1× EVDO) and ultra mobile broadband (UMB) systems. The 3rd generation partnership project (3GPP) developed wideband code division multiple access (WCDMA), high speed packet access (HSPA) and long term evolution (LTE) systems. The institute of electrical and electronics engineers developed mobile worldwide interoperability for microwave access (WiMAX) systems. As number of users of mobile communication is increasing along with number of services provided over these systems, there is a need of mobile communication with large capacity, high throughput, lower latency and better reliability.
super mobile broadband (SMB) system based on millimeter waves i.e. radio waves with wavelength in the range of 1 millimeter (mm) to 10 mm, which corresponds to a radio frequency of 30 gigahertz (GHz) to 300 GHz, is a candidate for next generation mobile communication technology as vast amount of spectrum is available in mmWave band. An SMB network consists of multiple SMB base stations (BSs) that cover a geographic area. In order to ensure good coverage, SMB base stations need to be deployed with higher density than macro-cellular base stations. In general, roughly the same site-to-site distance as microcell or Pico-cell deployment in an urban environment is recommended. At higher frequency the propagation path losses are higher and hence the propagation distance is shorter. Beamforming techniques are used to decrease the high path loss and to increase the propagation distance for communication at higher frequency. Beamforming can be classified into transmission (TX) beamforming performed in a transmitting end and reception (RX) beamforming performed in a receiving end. In general, the TX beamforming increases directivity by narrowing an area in which the propagation is directed by using a plurality of antennas. In this situation, aggregation of the plurality of antennas can be referred to as an antenna array, and each antenna included in the array can be referred to as an array element.
The antenna array can be configured in various forms such as a linear array, a planar array, etc. The use of the TX beamforming results in the increase in the directivity of a signal, thereby increasing a propagation distance. Further, since the signal is almost not transmitted in a direction other than a directivity direction, a signal interference acting on another receiving end is significantly decreased. The receiving end can perform beamforming on a RX signal by using a RX antenna array. The RX beamforming increases RX signal strength in a specific direction by increasing the antenna gain in a specific direction, and excludes a signal transmitted in a direction other than the specific direction from the RX signal, thereby providing an effect of blocking an interference signal.
The frame structure for one such wireless communication using beamforming technique is illustrated in FIG. 1. The BS transmits a synchronization signal through a synchronization channel (SCH) which assists MS to detect the presence of base station. The BS also transmits broadcast signal through a broadcast channel (BCH). The BCH carries essential system information which enables MS to have initial communication with the BS. The SCH and BCH are transmitted repetitively by performing beamforming on the channels with different transmission beams wherein each TX beam transmits the SCH and BCH in different direction. Because of hardware limitation of one antenna array at the BS (one antenna array is needed for one beam direction) the TX beams in different directions are transmitted at different times. The mobile station (MS) uses receive beamforming to detect the synchronization signal. The mobile station (MS) uses multiple RX beams to detect the SCH transmitted using multiple TX beams. Consider for example, SCH and BCH is transmitted using four TX beams and MS uses four RX beams to search the SCH and BCH. Four TX beams are transmitted in four different time durations (e.g., slots) in a sub frame on the high frequency carrier as illustrated in FIG. 1.